Smear leaf and dish
with Vaseline. Place the leaf in the middle of the dish. Mix Plaster of
Paris and pour over leaf. Wait 10 minutes. Turn out.

Hints:

Real fossils are made
in a few different ways. This method simulates what is known as the “Moulds
or casts” where a shell embedded in a rock may be dissolved by ground
water and leave a cavity preserving the shape of the shell. This is a natural
external mould or imprint of the shell’s exterior.